1. Field of the Invention
The present invention relates to an Al—Ni-rare earth element alloy sputtering target, and more particularly, to such an Al—Ni-rare earth element alloy sputtering target which can be produced favorably even when the target is to be made large and with which it is possible to realize stable sputtering which does not accompany major warp of the target.
While the sputtering target according to the present invention is applicable to an interconnection film which forms a liquid crystal panel, an organic EL panel or the like for use in a television set, a laptop computer, a monitor or other display, a reflection film, a recording film and the like for use in the field of optical recording, an interconnection film and the like in the field of semiconductor devices, use of the sputtering target according to the present invention for a liquid crystal panel will be described below as a typical application.
2. Description of the Related Art
A liquid crystal panel of the active matrix type includes a TFT array substrate which uses thin film transistors (TFTs) as switching elements and includes pixel electrodes (transparent conductive film) and interconnection portions which may be scanning lines, signal lines and the like, an opposed substrate which includes a common electrode and is disposed over a predetermined distance facing the TFT array substrate, and a liquid crystal layer which is injected between the TFT array substrate and the opposed substrate.
The signal lines in the liquid crystal panel are sections which are electrically connected with the pixel electrodes, and are generally made of aluminum alloy. However, direct contact of the aluminum alloy (film) and the pixel electrodes produces aluminum oxide or the like, which is an insulation material, at the interface between the two and increases the electrical resistance there, a conventional solution to which is generally interposition of a film of refractory metal, such as Mo, Cr, Ti and W, as barrier metal between the aluminum alloy and the pixel electrodes. In the meantime, the recent years have seen an attempt for a simplified producing process by means of omission of such a film of high-melting-point metal and direct connection of the signal lines (aluminum alloy) and the pixel electrodes (transparent conductive film), and use of Al—Ni alloy for example as the aluminum alloy has been proposed for reduction of the insulation material such as aluminum oxide and hence reduction of the electrical resistance (Patent Document 1; JP, 2004-214606, A). Patent Document 1 also describes addition of Nd, Y, Fe or the like as the third element makes it possible to enhance the heat resisting property of the interconnection film and improve the electrical characteristics owing to smaller crystal grains and smaller intermetallic compounds in the structure.
Sputtering is generally used to form a thin film such as the interconnection film above. Sputtering is a method according to which plasma discharge is developed between a substrate and a target material which serves as a film material, gas ionized by the plasma discharge collides with the target material, the atoms of the target material are ejected and accumulated as a thin film on the substrate and is advantageous in that it achieves production of a thin film of the same composition as that of the target material unlike where a vacuum deposition or AIP method is used.
Targets for production of the aluminum alloy film which have been so far proposed include the aluminum alloy having substantially reduced crystal grain diameters according to Patent Document 2 (JP, 11-106905, A), very fine compounds as those described in Patent Document 3 (JP, 2001-214261, A), Patent Document 4 (JP, 10-199830, A), etc. It is shown that remarkably fine and small crystal grains or compounds reduce splashing during film deposition and secure the uniform composition and film thickness of the thin resultant film.
By the way, while the larger size of a liquid crystal display panel or the like urgently demands increase of the size of a target for fabrication of the liquid crystal display panel, manufacturing of a large-size target still needs reduced splashing, better characteristics of a thin film to produce, and additionally, suppressed warp of the target attributable to heating during producing or use.
Warp of the target which occurs during producing may be warp of a plate at the stage of mechanical processing due to the residual stress which remains after rolling or straightening, thermal deformation during bonding to a cooling plate, etc., and if such deformation is excessive, not only the accuracy of the product but the productivity as well deteriorate. Meanwhile, thermal deformation which occurs during use includes deformation caused by repeated heating and cooling during film deposition, and such excessive deformation during use causes a problem that a solder material which bonds the target with the cooling plate cracks, the target locally fails to get cooled and the solder material melts and gets peeled off from the cooling plate.
The present invention has been made in light of the problems above, and accordingly, aims at providing an Al—Ni-rare earth element alloy sputtering target which does not accompany major deformation (warp) during producing and use, and can be produced precisely and efficiently even when the target is to be made large, and with which it is possible to realize stable film deposition.